Buggy code:
public class MMSClient { private String mOAuthClientId ; private String mOAuthSecret ; private String mDevUser ; private String mDevPasswd ; private String mUserName ; private String mUserPasswd ; private String mUserId ; private String mDevToken ; private String mAppToken ; private String mUserToken ; private final transient MaxRestServiceImpl mMaxService ; private transient MMXSettings mSettings ; private transient User mUser ; private transient Device mDevice ; private transient MMSClient . MMSAdmin mAdmin ; public class MMSAdmin { MMSAdmin ( ) { } public Client createApp ( String appName , String description , String appPasswd , String ownerEmail ) throws MaxServiceException , IOException , OAuthSystemException { } public void saveApp ( Client client , MMXSettings settings ) { } public Client getApp ( String clientId ) throws MaxServiceException , IOException { } public User getUserByName ( String userName ) throws MaxServiceException , IOException { } public List < User > getUsers ( int offset , int count ) throws IOException { } public void uploadApnsCertificate ( String clientId , String certPasswd , byte [ ] cert , boolean production ) throws MaxServiceException , IOException { } } private static boolean isEmpty ( String str ) { } public MMSClient ( MMXSettings settings ) { } public MMSClient ( MMXSettings settings , String baseUrl ) { } public boolean isAdminAuthenticated ( ) { } public boolean isAppAuthenticated ( ) { } public boolean isUserAuthenticated ( ) { } public MMSClient . MMSAdmin getAdmin ( String devUser , String devPasswd ) { } public MMSClient . MMSAdmin getAdmin ( ) { } public boolean authApp ( ) throws MaxServiceException , IOException { } public void authUser ( String userName , String userPasswd , String deviceId ) throws MaxServiceException , IOException { } public String registerUser ( User user ) throws MaxServiceException , IOException { if ( ( ! ( isAppAuthenticated ( ) ) ) && ( ! ( authApp ( ) ) ) ) { throw new SecurityException ( "Curernt<seq2seq4repair_space>app<seq2seq4repair_space>has<seq2seq4repair_space>no<seq2seq4repair_space>authentication<seq2seq4repair_space>info" ) ; } mMaxService . registerUser ( mAppToken , user ) ; StringBuilder name = new StringBuilder ( ) ; if ( ! ( MMSClient . isEmpty ( user . getFirstName ( ) ) ) ) { <START_BUG> name . append ( name ) ; <END_BUG> } if ( ! ( MMSClient . isEmpty ( user . getLastName ( ) ) ) ) { if ( ( name . length ( ) ) > 0 ) { name . append ( '<seq2seq4repair_space>' ) ; } name . append ( user . getLastName ( ) ) ; } mUserId = user . getUserIdentifier ( ) ; mSettings . setString ( PROP_USER , user . getUserName ( ) ) ; mSettings . setString ( PROP_NAME , name . toString ( ) ) ; mSettings . setString ( PROP_PASSWD , user . getPassword ( ) ) ; mSettings . setString ( PROP_EMAIL , user . getEmail ( ) ) ; mSettings . setString ( PROP_MMSUSERID , mUserId ) ; mSettings . save ( ) ; return mUserId ; } public String registerAndAuthenticate ( User user , String deviceId ) throws MaxServiceException , IOException { } public User getCurrentUser ( ) throws MaxServiceException , IOException { } public String getUserId ( ) { } public String getUserToken ( ) { } }

Fix:
name . append ( user . getFirstName ( ) ) ;